U.S. Pat. No. 3,007,891 discloses the addition of carbon black and dispersing agent of small molecular weight in the esterification reaction. However, it is necessary to use precipitation, centrifugation, and filtration in order to remove a large amount of agglomerates of carbon black before continuing polymerization in order to obtain black masterbatch. However, this black masterbatch contains only 1-10% of carbon black by weight and often contaminates the reactor or reactor piping.
U.S. Pat. No. 4,116,924 teaches using fragile dispersing hydrocarbonic resin or rosin oil resin with a softening point between 70.degree.-195.degree. C. and copolymer with a melting point between 140.degree.-200.degree. C. to manufacture black masterbatch with high concentration. According to this patent, carbon black is first charged into a mill with cationic surfactant and water, ground into colloidal-like fluid aqueous dispersion of carbon black, and then charged with dispersive resin under the control of PH value at a predetermined range. Thereafter, the water is removed and the dried material is blended with copolyester through an extruder to form pellets. However, the manufacture and treatment of the dispersing liquid is relatively complicated.
U.S. Pat. Nos. 3,905,937 and 4,001,171 disclose utilizing compounds which are complicated in structure and difficult to obtain as the dispersing agent.
U.S. Pat. Nos. 3,905,937, 4,001,171, 4,279,902 and 4,379,871 teach the addition of organic solvent in the manufacturing process so that the organic solvent must be removed or retrieved as the process has been completed thereby making the manufacturing process difficult and complicated.
U.S. Pat. Nos. 4,879,335 and 5,106,905 disclose mixing carbon black with liquid polyester to form liquid coloring agent for polyester spinning. However, the liquid coloring agent will lower the viscosity of the spinning polyester and will not have sufficient thermal stability at the spinning temperature between 280.degree.-300.degree. C. so that the liquid coloring agent will be degraded into gas with smaller molecular weight. Further, the polyester will turn to be yellow in color and the filament breakage rate will be increased. In addition, there will be badly influence to the strength, stretch ability, and heat resistance of the fiber.
Japanese Publication No. 49-87792 and U.S. Pat. No. 4,208,318 suggest addition of a small amount of chemically modified metal phthalocyanine so as to make the color concentrate have a slight bluish tone. However, the chemically modified metal phthalocyanine is too expensive to use it.
Therefore, it is an object of the present invention to provide a black masterbatch which can obviate and mitigate the above-mentioned drawbacks.